Chromatography columns often contain a net to prevent media from escaping from the end cells which are used for radially distributing the fluid flowing in from a central inlet at one end of the column and for radially collecting the fluid for subsequent outputting from a central outlet at the opposite end of the column. These nets extend across substantially the whole internal diameter of the column. In the prior art the nets have been made of polymer materials and have been attached (with a supporting backing plate if required) to the central inlet resp. central outlet by means of screws or bolts. The screws or bolts are mounted with their heads on the side of the net facing away from the inlet, resp. outlet, and they pass through suitably sized holes in the net and are screwed into suitably threaded axial holes in the wall of the central inlet resp. outlet.
Alternatively nets have been attached by being mounted on a central inlet or outlet tubular port provided with an internal thread and a stop flange positioned on the outside of the port at a distance from the end where the net is to be mounted which is less than the thickness of the net. The net is then positioned against the flange with the end of the port extending into a central opening in the net. The net is held in place by a threaded end piece which has a tubular portion provided with a thread adapted to mate with the thread on the inside of the port, and a flange at one end which pushes the net against the flange on the port when the end piece is screwed up into the port.
One problem with existing arrangements is that it is difficult to give the net proper support, due to the flexible nature of the net. As a consequence, the net may bend if the flow of sample media through the cell is high. In fact, it is common that the net bends to such an extent that it gets plastically deformed, which is highly undesirable as it influences the characteristics of the bed and thus the flow characteristics for the sample. Therefore, the net limits the flow for such columns.
Another problem is that the heads of the mounting screws, resp. the end pieces, project into the bed media and interfere with the packing of the bed media. This may also lead to undesirable fluid-flow characteristics at the top/bottom of the bed.
The heads may also cause dead volumes, i.e. spaces where fluid circulation is slow or non-existent, where particles can collect and this makes cleaning difficult and can lead to sanitary problems.
As used herein and in the appended claims: The term “fluid system” is intended to designate the apparatus in which liquid is either introduced to or withdrawn from a cell at a zone approximately transverse the direction of flow through the cell. The term “cell” is intended to include the terms “vessel” and “column”, as well as any other structure utilised by practitioners of the separation arts, to effect a separation and/or extraction of components from an admixture by bringing the admixture into contact with solid or liquid exchange media, above referred to as the packing. “Cross-sectional zone” (or region) refers to a region within a cell bounded by cross sections of the cell-oriented transverse (typically approximately normal) the longitudinal direction of flow through the cell. “Longitudinal direction of flow” refers to the direction of flow from an inlet towards an outlet within a cell. “Longitudinal” is used consistently to designate the dominant flow path of fluid through a cell without regard to direction. “Flow connection system” refers to a system of channels or paths that connect two points in a fluid circuit. While the skilled person realises that columns may be arranged in many different orientations, for the sake of convenience and clarity of description, it will be assumed that the upper end of the column is the inlet end while the bottom end is the outlet end. “Distribution system” refers to structure through which fluids are introduced to a cell and “collection system” refers to structure used to withdraw fluids from a cell, in each instance from a cross-sectional zone.